In a principal aspect, the present invention relates to a spray drying process for preparation of discrete nanosized particles, such as CaF2 particles, that are not agglomerated.
Calcium fluoride (CaF2) or ‘CaF2-like’ materials are of significant interest in caries prevention as they have been suggested to be the major source of labile fluoride (F) in the oral environment after F treatments. The release of F from the labile store of loosely bound F in the oral cavity environment increases the mineral saturation of oral fluid, and can promote the repair of lesions and reduce demineralization during cariogenic attack. However, a conventional sodium fluoride (NaF) rinse can only lead to very small amounts of CaF2 deposit formation due to the low concentration of free calcium (Ca) ions in the mouth. In contrast, more CaF2 deposits in the oral environment have been found to significantly increase the remineralization effects of the F treatment without increasing the F levels.
Previously reported is the preparation of a nano CaF2 that has a theoretical spherical particle size of 41 nm based on BET (Brunauer-Emmett-Teller) surface area measurements. When used as the F source in an oral rise, these nano CaF2 were shown to produce a greater F deposition than a NaF rinse of the same F dose in both in vitro and in vivo studies. However, electron microscopic observations indicated that the CaF2 material consisted primarily of CaF2 agglomerates, about 300 nm to 800 nm in size, but that the agglomerates, were made up of much small primary CaF2 particles of <50 nm in size. These agglomerates were not readily dispersed into the primary CaF2 particles by ultrasound processing, indicating that the primary CaF2 particles in each cluster were tightly held together. However, there is strong evidence that significantly greater F efficacies can be achieved if the nano CaF2 or agglomerates can be dispersed into the smaller primary particles. Unwanted agglomeration of nanoparticles due either to the preparation process or post synthesis treatments has thus remained a problem.